Quantum metrology has many important applications in science and technology, ranging from frequency spectroscopy to gravitational wave detection. Quantum mechanics imposes a fundamental limit on measurement precision, called the Heisenberg limit, which can be achieved for noiseless quantum systems, but is not achievable in general for systems subject to noise. Here we study how measurement precision can be enhanced through quantum error correction, a general method for protecting a quantum system from the damaging effects of noise. We find a necessary and sufficient condition for achieving the Heisenberg limit using quantum probes subject to Markovian noise, assuming that noiseless ancilla systems are available, and that fast, accurate quantum processing can be performed. When the sufficient condition is satisfied, a quantum error-correcting code can be constructed that suppresses the noise without obscuring the signal; the optimal code, achieving the best possible precision, can be found by solving a semidefinite program.

Open quantum systems can have exceptional points (EPs), degeneracies where both eigenvalues and eigenvectors coalesce. Recently, it has been proposed and demonstrated that EPs can enhance the performance of sensors in terms of amplification of a detected signal. However, typically amplification of signals also increases the system noise, and it has not yet been shown that an EP sensor can have improved signal to noise performance. We develop a quantum noise theory to calculate the signal-to-noise performance of an EP sensor. We use the quantum Fisher information to extract a lower bound for the signal-to-noise ratio(SNR) and show that parametrically improved SNR is possible. Finally, we construct a specific experimental protocol for sensing using an EP amplifier near its lasing threshold and heterodyne signal detection to achieves the optimal scaling predicted by the Fisher bound. Our results can be generalized to higher order EPs for any bosonic non-Hermitian system with linear interactions.

Modular quantum computing architectures require fast and efficient distribution of quantum information through propagating signals. Here we report rapid, on-demand quantum state transfer between two remote superconducting cavity quantum memories through traveling microwave photons. We demonstrate a quantum communication channel by deterministic transfer of quantum bits with 76% fidelity. Heralding on errors induced by experimental imperfection can improve this to 87% with a success probability of 0.87. By partial transfer of a microwave photon, we generate remote entanglement at a rate that exceeds photon loss in either memory by more than a factor of three. We further show the transfer of quantum error correction code words that will allow deterministic mitigation of photon loss. These results pave the way for scaling superconducting quantum devices through modular quantum networks.The assembly of large-scale quantum machines hinges on the ability to coherently connect individually controlled quantum storage elements. Quantum networkswherein small, highly coherent modules can exchange quantum information via propagating photons-present a promising approach to achieve this connectivity [1]. Such networks allow for bottom-up construction of reconfigurable quantum systems, forming a backbone for fault-tolerant modular quantum computers [2][3][4]. A crucial challenge, however, is presented by inefficiencies in the mapping of stored quantum information onto traveling signals as well as those during the subsequent photon transfer. Primarily because these inefficiencies have so far been large, quantum communication between remote memories has only been achieved probabilistically [5][6][7][8][9][10][11], requiring local storage of quantum information on long time scales in order for a network to be scalable [12]. Even simple protocols, such as transferring a single quantum bit in a network, have been executed at rates that are orders of magnitude slower than available coherence times [13,14].Direct quantum state transfer, which can be rapid and deterministic, is a desirable scheme for quantum communication within a scalable network [15]. In this protocol, a sending system emits a quantum state as a shaped photonic wavepacket that is then absorbed by a receiving system. This requires strong, tunable coupling between light and matter, as well as efficient transfer of photons at a shared communication frequency; so far, state transfer in optical networks has been highly probabilistic due to inefficiencies in photon coupling and transfer [7].can combine low loss with strong coupling. This platform is well-suited to realize on-demand state transfer, and thus to scale quantum devices in a modular fashion. To this end, superconducting microwave memories and propagating modes have successfully been interfaced to realize controlled photon emission [16][17][18][19] and absorption [20][21][22] independently. Due to the difficulty posed by the need for efficient, frequency-matched photon transfer, however, the goal of deterministic...

Electromagnetically induced transparency, as a quantum interference effect to eliminate optical absorption in an opaque medium, has found extensive applications in slow light generation, optical storage, frequency conversion, optical quantum memory as well as enhanced nonlinear interactions at the few-photon level in all kinds of systems. Recently, there have been great interests in exceptional points, a spectral singularity that could be reached by tuning various parameters in open systems, to render unusual features to the physical systems, such as optical states with chirality. Here we theoretically and experimentally study transparency and absorption modulated by chiral optical states at exceptional points in an indirectly-coupled resonator system. By tuning one resonator to an exceptional point, transparency or absorption occurs depending on the chirality of the eigenstate. Our results demonstrate a new strategy to manipulate the light flow and the spectra of a photonic resonator system by exploiting a discrete optical state associated with specific chirality at an exceptional point as a unique control bit, which opens up a new horizon of controlling slow light using optical states. Compatible with the idea of state control in quantum gate operation, this strategy hence bridges optical computing and storage.

Nanomaterials have been applied as antibacterial agents by virtue of their unique functioning mechanism different from that of conventional antibiotics. Cerium oxide nanoparticles (CeO 2 NPs) are important antibacterial agents due to their relatively low toxicity to normal cells and their distinct antibacterial mechanism based on the reversible conversion between two valence states of Ce(III)/ Ce(IV). Some studies have been conducted to explore their antibacterial activities; however, systematic research reviews on the related mechanisms and influencing factors are still quite rare. In this review, we discuss the plausible mechanisms of the antibacterial activity of CeO 2 NPs, analyze different influencing factors, and summarize various research reports on antibacterial effects on E. coli and S. aureus. We also propose the potential applications and prospects, and hope to provide an in-depth understanding on the antibacterial mechanism and a better guidance to the design and applications of this promising antibacterial material in the future.

Quantum state transfer between microwave and optical frequencies is essential for connecting superconducting quantum circuits to coherent optical systems and extending microwave quantum networks over long distances. To build such a hybrid "quantum Internet," an important experiment in the quantum regime is to entangle microwave and optical modes. Based on the model of a generic cavity electro-optomechanical system, we present a heralded scheme to generate entangled microwave-optical photon pairs, which can bypass the efficiency threshold for quantum channel capacity in direct transfer protocols. The preferable parameter regime for entanglement verification is identified. Our scheme is feasible given the latest experimental progress on electro-optomechanics, and can be potentially generalized to various physical systems.

Chronic wounds, such as the diabetic ulcer wounds have serious effect on people's lives, and can even lead to death. Diabetic ulcer wounds are different from normal wounds and much easier to be infected and induce oxidative stress due to the special surrounding microenvironment, which makes it necessary to prepare materials with antibacterial property and antioxidant activity simultaneously. The molybdenum disulfide‐ceria (MoS2‐CeO2) nanocomposite possesses both the photo‐thermal therapy (PTT) antibacterial capability of polyethylene glycol modified molybdenum disulfide nanosheets and the antioxidant activity of cerium dioxide nanoparticles (CeO2 NPs). By combining the inherent antibacterial activity of CeO2 NPs, the MoS2‐CeO2 nanocomposite exhibits excellent PTT antibacterial capability against both gram‐positive and gram‐negative bacteria through 808 nm laser treatment, thereby reducing the risk of wound infection. Owing to the abundant oxygen vacancies in CeO2 NPs, Ce3+ and Ce4+ can transform reversibly which endows MoS2‐CeO2 nanocomposite with remarkable antioxidant ability to clear away the excessive reactive oxygen species around the diabetic ulcer wounds and promote wound healing. The results demonstrate that MoS2‐CeO2 nanocomposite is a promising class for the clinical treatment of chronic wounds especially the diabetic ulcer wounds, and 808 nm laser can be used as a PTT antibacterial switch.

Communication over proven-secure quantum channels is potentially one of the most wide-ranging applications of currently developed quantum technologies. It is generally envisioned that in future quantum networks, separated nodes containing stationary solid-state or atomic qubits are connected via the exchange of optical photons over large distances. In this work we explore an intriguing alternative for quantum communication via all-microwave networks. To make this possible, we describe a general protocol for sending quantum states through thermal channels, even when the number of thermal photons in the channel is much larger than 1. The protocol can be implemented with state-of-the-art superconducting circuits and enables the transfer of quantum states over distances of about 100 m via microwave transmission lines cooled to only T = 4 K. This opens up new possibilities for quantum communication within and across buildings and, consequently, for the implementation of intra-city quantum networks based on microwave technology only.